The invention relates to a crossflow heat exchanger, including elements formed of ceramic material. Heat exchangers formed of ceramic materials have in the recent past frequently been proposed for high temperature heat transfer and/or with the use of corrosive heat-exchange media. The present status of technology is disclosed in the following documents:
European Patent Application No. 00 43 113 PA1 DE OS No. 29 37 342 PA1 DE OS No. 24 28 087 PA1 DE PS No. 25 10 893 PA1 DE OS No. 29 34 973 PA1 DE PS No. 27 07 290 PA1 DE PS No. 28 41 571 and PA1 DE PS No. 26 31 092.
Since such heat exchangers are typically suitable for temperatures up to 1,400.degree. C. and, according to the ceramic material employed, are resistant to corrosive media, they are particularly suitable for use in cases where highly heated corrosive gases require cooling or heating. Such ceramic heat exchangers can also be used where condensed phases arise in case of falling short of the dew point. Heat-exchanger modules as described in the last-mentioned publication, are in particular distinguished by a large heat-exchange surface and are available at reasonable prices due to the manufacturing process described.
In the case of conventional heat exchangers including elements formed of metal, only highest quality materials can be used for the manufacture of such heat exchangers, if they can be manufactured at all, with the result that heat transfer is in these cases only possible at extremely high cost.
The last-cited patent document, DE No. 26 31 092, describes a modular-structured heat-exchange element of ceramic material. The invention manages, by means of material selection and the selection of low layer thickness for the separating walls between the individual ducts arranged in layers at right angles to one another, to minimize the risk of damage due to temperature-fluctuations, which has up to now prevented the more widespread use of such ceramic heat exchangers, and simultaneously to maximize the heat-exchange surface available with a given volume. For commercial applications, for large volume throughputs, the individual elements must be formed of extremely large spatial dimensions. However, the manufacture of such large elements presents problems, since, on the one hand, the individual modules, consisting of "green" (unfired) ceramic mass, must be fired after assembly to produce a heat-exchange element. Large firing chambers and careful cooling processes are necessary for this purpose, in order to prevent the occurrence of cracking due to thermal stresses. On the other hand, such large elements can only be transported at extremely great risk. If damage occurs to such large elements, the entire element becomes useless.
In DE No. 26 31 092, the inventor achieves an enlargement of the heat-exchange surface and an enlargement of throughput of heat-exchange media by creating double-modules, which can be assembled to form a larger unit by means of a system of separating walls, In Patent Document DE No. 27 07 290, the invention discloses a heat exchanger, structured from individual elements, which can be assembled to form larger units with intermediate layers including ceramic-fibre material. Openings, through which the heat-exchange media flow, are provided to fit together precisely by means of a web and groove system.
In Patent Document DE No. 29 34 973, a heat-exchange element is provided by adhesively joining ribbed layers of ceramic material. The heat-exchange element thus obtained is then surrounded with a metallic casing consisting of plates. The plates are pressed by means of bolts, screws and springs against the side surfaces of the heat-exchange element, requiring the sealing materials to be resilient and flexible. This invention does not envisage the assembly of several heat-exchange elements to form a larger unit.
In Patent Document DE No. 25 10 893, discloses a recuperator, constructed of individual brick-shapes. In each case, two brick-shapes are employed to form a duct for one heat-exchange medium. Not until the third brick-shape is added is there a channel formed for a second heat-exchange medium. The assembly of a recuperator is carried out in accordance with the invention described in such a way that an existing chamber is lined with brick-shapes and wall-bricks. The brick-shapes fitting into one another by means of a tongue and groove system. Short-circuiting flow between the two heat exchanger media can be avoided where necessary by means of cementing using mortar. Due to the size of the brick-shapes, the ratio of heat-exchange surface to the volume of the recuperator is relatively small. Reduction in size of the ducts, which signifies an increase in the heat-exchange surface in a given volume, is practically impossible using the brick-shapes proposed, since, with decreasing brick-shape size, cementing becomes more and more difficult, and a technologically interesting ratio for heat-exchange surface to recuperator volume can thus not be achieved.
In Patent Document DE No. 29 37 342, a larger unit is assembled from individual heat-exchange elements, which are clamped against one another by means of bolts, screws, and springs.
European Patent Application No. 0 043 113 discloses a crossflow heat exchanger consisting of ceramic heat exchanger modules which are pressed against one another by means of a clamping mechanism, consisting of screws, bolts, and springs, and thus brought into gastight contact.